This application is a continuation-in-part of my now abandoned application Ser. No. 504,889, entitled "Rooted Aerodynamic Blade and Elastic Retainer Construction," filed Sept. 11, 1974 and assigned to the same assignee as the present application and invention, to wit: Avco Corporation.
The present invention comprises a novel damped aerodynamic blade and elastic roll pin construction for use in dynamic rotating machinery, for example, axial flow compressors and turbines. In rotating machinery of this kind the attachment of the individually shaped blades to the rotor discs presents difficult mechanical design problems. These problems typically arise and are here considered in the general environment of axial flow compressors.
Going back into the history of turbine blade attachments one finds common types referred to as "fir-tree" and "dove-tail."
In some prior art structures a pin is passed through the blade root and the rotor disc to provide attachment. The pin-type structure of U.S. Pat. No. 3,400,912 to Carta and Stargardter, issued Sept. 10, 1968, features a variation of root dimensions, and/or the radial position of the pin, from blade to blade in order to lessen undesired effects of resonance.
An interesting construction of the dove-tail type is that of U.S. Pat. No. 1,619,133 to Kasley issued Mar. 1, 1927. In the Kasley construction the slots in the turbine disc are longitudinal and not transverse.
In the structure of U.S. Pat. No. 2,595,829 to Dean, issued May 6, 1952, the blade root portions are semicircular and positioned in conforming sockets. Under the root of each blade is a resilient cushion or dampening member which urges the convex blade root against the concave socket. The dampening member yields sufficiently to permit the blade to pivot slightly in the socket. The filler material is such that the Dean structure is a relatively low-speed device.
In the structure of U.S. Pat. No. 2,686,655, to Schorner, issued Aug. 17, 1954, the blades are ceramic and positively located by spacing pieces. A thermally balanced joint is shown.
Reference is now made to the U.S. Pat. No. 2,727,716 to Feilden et al, issued Dec. 20, 1955. In the structure there shown each blade is rendered tiltable by a flexible tension element serving as an anchor. Synthetic rubber damping elements are there featured. Arrangements of this type involve stress risers and are limited as to maximum speed.
The structure of U.S. Pat. No. 2,753,149 to Kurti, issued July 3, 1956, is of the fir-tree type with a retaining shank. The clearance around the shank is such as to permit tilting of the blade. This patent is primarily concerned with the axial locking of blades.
U.S. Pat. No. 2,847,187 to Murphy, issued Aug. 12, 1958, features a blade locking piece in resilient strip form. West German Patent No. 950,557, published Oct. 11, 1956, shows a pine-tree root structure similar to that of Kurti, featuring a boltlike retainer and complementary surfaces on blade and disc for permitting limited tilting. West German Patent No. 632,001, published July 1, 1936, shows an arrangement in which contact surfaces between blade and disc deform. Italian Patent No. 312,864, granted Nov. 28, 1933, features an arrangement in which a wedge is inserted between the base of the disc slot and the bottom of the blade.
The blade arrangement in U.S. Pat. No. 3,720,481 to Motta, issued Mar. 13, 1973, employs a split bushing to accomplish a secure locking of the blade root. The blade spacer of the U.S. Pat. No. 3,572,970 to Smuland, issued Mar. 30, 1971, performs a radial locking function and is made oversize for that purpose. In the structure of U.S. Pat. No. 2,936,155 to Howell et al, issued May 10, 1960, the split pin provides a rigid support for the blade.
The construction disclosed in the U.S. Pat. No. 2,997,274 to Hanson, issued Aug. 22, 1961, shows pins for damping purposes but the pins are either a duality or extended in a radial direction. The structure of British Pat. No. 753,229, complete specification published July 18, 1956, is directed to the seating of ceramic blades.